Fix AnimationParser remove_prefix test

The test fails because TEST_STRING, a char[], is silently
converted to a std::string, passed to remove_prefix, then
the string is destroyed, but a pointer to the string is
returned.

Fix it by changing the signature of remove_prefix to use
std::string_view to be more robust in handling raw char*.

Test: run it
Change-Id: I553c066907f09cf330c8b7a4659db5a1fee82cac